1. Technical Field
The present invention relates to a radiographic apparatus using a solid-state imaging device.
2. Background Art
Apparatuses that irradiate an object with X-rays and detect an intensity distribution of X-rays transmitted through the object to obtain a radiographic image of the object are widely used in industrial nondestructive testing and in medical diagnosis. Commonly used methods of such photography include a film/screen method for X-rays. The film/screen method involves performing photography by combining a photographic sensitive film with phosphor that is X-ray sensitive. Phosphor, a rare earth that emits light when irradiated by X-rays, is formed into a sheet and appressed against both faces of a photographic sensitive film. X-rays transmitted through an object are converted into visible light by the phosphor, whereby the light is captured by the photographic sensitive film. Visualization is achieved by developing a latent image formed on the film by chemical processing.
Moreover, recent progresses in digital technology has led to the widespread use of a method where an intensity distribution of X-rays transmitted through an object is converted into and detected as an electric signal, whereby the electric signal is processed and reproduced on a monitor or the like as a visible image to obtain a high-definition radiographic image. As a method for converting such a radiographic image into an electric signal, a radiographic image recording/reproducing system has been proposed in which X-rays transmitted through an object are temporarily accumulated in phosphor as a latent image and an excitation light such as laser light is subsequently irradiated to photoelectrically read out and output the latent image as a visible image.
Furthermore, with recent progress in semiconductor process technology, apparatuses that photograph a radiographic image in the same manner using a semiconductor sensor have been developed. Such systems have a significantly wider dynamic range than conventional X-ray photography systems using a photographic sensitive film and are pragmatically advantageous in that radiographic images not affected by variances in an amount of X-ray exposure can be obtained. At the same time, unlike conventional photographic sensitive film systems, chemical processing is not required. Accordingly, there is another advantage that output images can be obtained instantaneously. Such systems are advantageous in that, unlike the aforementioned radiographic image recording/reproducing systems that read out images in a subsequent process, images can be instantaneously displayed on a monitor. Furthermore, portable radiographic apparatuses have also been developed and are used in situations that require photographs to be taken in arbitrary shooting postures.
In regards to such a portable radiographic apparatus, Japanese Patent No. 3382227 (hereinafter referred to as Document 1) proposes a structure in which boards (substrates) and the like are laminated in an X-ray incidence direction of an X-ray detection sensor for purposes of thinning and weight saving. In addition, Japanese Patent Laid-Open No. 2003-014855 (hereinafter, Document 2) proposes achieving weight saving in a portable radiographic apparatus by laminating boards and the like in an X-ray incidence direction and reducing use of an X-ray shielding member (having a high specific gravity) that protects the boards from X-rays.
Generally, increasing an intrinsic strength of an apparatus while protecting the inside of the apparatus results in the apparatus itself becoming heavier and bigger. With a portable radiographic apparatus, there may be cases where photography is performed by inserting the apparatus under a subject, such as photography of a subject on a table in an X-ray room, a subject on a ward bed, or a subject on an operating table in an operating room. Therefore, in the interest of reducing the strain on patients, thinning of portable radiographic apparatuses is required. In addition, when inserting a radiographic apparatus under a subject during photography, an X-ray technician operating the radiographic apparatus is required to hold the apparatus with one hand. In particular, when a radiographic apparatus is used at the bedside in wards by a technician making ward rounds on a visiting car, the technician must set the radiographic apparatus while single-handedly maintaining the posture of a patient. Therefore, downsizing and weight saving are essential in order to similarly reduce the strain on technicians as well. As seen, portable radiographic apparatuses are faced with issues that conflict with the perspective of protecting the apparatus, namely, thinning from the perspective of reducing the strain on patients and weight saving from the perspective of reducing the strain on operators.
However, with the apparatus cited in Document 1, a board for driving a sensor, a board for processing a signal acquired by an X-ray detection sensor, and the like are all arranged on an underside. Therefore, there is a limit to how much the thickness of the radiographic apparatus itself can be reduced. In addition, a photographic unit itself must be strong enough to protect the X-ray detection sensor from external force. However, in the structure proposed in Document 1, since a portion in which the boards are arranged becomes a space, strength declines. Maintaining strength requires reinforcement such as inserting a member having a predetermined strength to an underside of the X-ray detection sensor. Consequently, a limit is posed with respect to achieving thinning.
Furthermore, with the apparatus proposed in Document 2, a drive circuit board and a signal processing circuit board for processing a signal obtained from a sensor are arranged in parallel with respect to an X-ray detection sensor. As a result, unlike Document 1, thinning can be realized. However, since boards are arranged in a planar direction, a limit is posed with respect to downsizing.